Enable using the toolchain (llvm) provided FileCheck.

SConstruct

Index: SConstruct
diff --git a/SConstruct b/SConstruct
index 218d489aee0d941e9ce9618228013a6f1a85eae0..271e637c16fe937d154e11b53ce65ecee53e17d4 100755
--- a/SConstruct
+++ b/SConstruct
@@ -1625,7 +1625,8 @@ def CommandTestFileDumpCheck(env,
                              name,
                              target,
                              check_file,
-                             objdump_flags):
+                             objdump_flags,
+                             use_llvm_filecheck=False):
   """Create a test that disassembles a binary (|target|) and checks for
   patterns in the |check_file|.  Disassembly is done using |objdump_flags|.
   """
@@ -1639,21 +1640,28 @@ def CommandTestFileDumpCheck(env,
   target = env.GetTranslatedNexe(target)
   return env.CommandTestFileCheck(name,
                                   ['${OBJDUMP}', objdump_flags, target],
-                                  check_file)
+                                  check_file, use_llvm_filecheck)
 
 pre_base_env.AddMethod(CommandTestFileDumpCheck)
 
-
-def CommandTestFileCheck(env, name, cmd, check_file):
+def CommandTestFileCheck(env, name, cmd, check_file, use_llvm_filecheck=False):
   """Create a test that runs a |cmd| (array of strings),
   which is expected to print to stdout.  The results
   of stdout will then be piped to the file_check.py tool which
   will search for the regexes specified in |check_file|. """
 
-  return env.CommandTest(name,
+  if use_llvm_filecheck:
+    return env.CommandTest(name,
+                         ['${PYTHON}',
+                          env.File('${SCONSTRUCT_DIR}/tools/llvm_file_check_wrapper.py'),
+                         '${FILECHECK}',
+                         check_file] + cmd,
+                         direct_emulation=False)
+  else:
+    return env.CommandTest(name,
                          ['${PYTHON}',
-                          env.File('${SCONSTRUCT_DIR}/tools/file_check.py'),
-                          check_file] + cmd,
+                         env.File('${SCONSTRUCT_DIR}/tools/file_check.py'),
+                         check_file] + cmd,
                          # don't run ${PYTHON} under the emulator.
                          direct_emulation=False)